Electrophotographic photoconductor

ABSTRACT

An electrophotographic photoconductor is composed of an electroconductive substrate, and a photoconductive layer, formed thereon, which contains a charge generating material, and a vinylidene compound of formula (I): ##STR1## wherein Ar represents a metallocene group; and X represents cyano group, an alkyl group having 1 to 8 carbon atoms, or an alkoxycarbonyl group represented by --COOC n  H 2n+1 , in which n is an integer of 1 to 8; or a vinylidene compound of formula (II): 
     
         Ar--CH═C(COOR).sub.2                                   (II) 
    
     wherein Ar represents a metallocene group; and R represents an alkyl group having 1 to 8 carbon atoms, which may form a ring in combination of two of the alkyl groups, each of these vinylidene compounds serving as a charge transporting material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic photoconductor,and more particularly to an electrophotographic photoconductor whichcomprises a vinylidene compound serving as a charge transportingmaterial.

2. Discussion of Background

Conventionally, an inorganic photoconductive material such as selenium,selenium - tellurium alloy, or zinc oxide has been widely used for aphotoconductive layer of an electrophotographic photoconductor.Recently, studies of electrophotographic photoconductors comprisingorganic photoconductive materials are made, and some of them are used inpractice. Of the above-mentioned organic electrophotographicphotoconductors, laminate-type electrophotographic photoconductors aremostly put to practical use, in which photoconductors a photoconductivelayer comprises a charge generation layer and a charge transport layer.Owing to such a function-separating photoconductive layer, there isimprovement in the photosensitivity and the life span of thephotoconductor comprising the organic material, which are conventionallyregarded as disadvantageous as compared with the photoconductorcomprising the inorganic material. Therefore, the electrophotographicphotoconductors comprising the organic photoconductive material havebeen actively developed, with taking full advantage of the merits forthe organic photoconductive material, that is, low cost, safety anddiversity.

The above-mentioned laminate-type electrophotographic photoconductorgenerally comprises an electroconductive substrate, and a chargegeneration layer comprising a charge generating material such as apigment or a dye, and a charge transport layer comprising a chargetransporting material such as hydrazone or pyrazoline, which layers aresuccessively overlaid on the electroconductive substrate. The chargetransporting material contained in the charge transport layer is anelectron-donor material, so that the above-mentioned photoconductor isof positive-hole-transfer type. Therefore, when the surface of thephotoconductor is negatively charged, it exhibits the photosensitivity.However, corona discharge is unstable when used for negatively chargingthe photoconductor as compared with when used for positively chargingthe same. The amount of ozone or nitrogen oxides generated in the courseof negative charging by the corona discharge is about 10 times thatgenerated in the course of positive charging. Those products areattached to the surface of the photoconductor, so that thephotoconductor physically and chemically deteriorates. Furthermore,those products cause the environmental problem.

In addition to the above-mentioned problems, to carry out thedevelopment of the negatively-chargeable photoconductor, a positivetoner is necessitated. However, from the viewpoint of a triboelectricseries, it is difficult to produce such a toner having a positivepolarity as can be used with ferromagnetic carrier particles. In atwo-component high-resistivity magnetic brush development method,therefore, negatively-chargeable toner is more stable and can be morefreely selected and used as compared with the positively-chargeabletoner. In this regard, a positively-chargeable photoconductor is moreadvantageous and can be more widely used than the negatively-chargeablephotoconductor.

With the above-mentioned advantages of the positive-chargeablephotoconductor taken into consideration, there are proposedpositively-chargeable photoconductors comprising the organicphotoconductive materials. For example, it is proposed that a chargetransporting material having a high electron-transporting capabilitysuch as 2,4,7-trinitro-9-fluorenone be contained in a charge transportlayer when the photoconductor is formed by laminating a charge transportlayer on a charge generation layer. However, this compound hascarcinogenicity, so that the above-mentioned photoconductor is extremelyunsuitable for use in practice from the viewpoint of industrial hygiene.

Moreover, U.S. Pat. No. 3,615,414 discloses a positively-chargeablephotoconductor comprising a thiapyrylium salt serving as a chargegenerating material which forms an eutectic complex by combining withpolycarbonate serving as a binder resin. However, the above-mentionedphotoconductor has the shortcoming that a memory phenomenon tends tooccur, and therefore ghost images are easily obtained.

It is possible to prepare a positively-chargeable photoconductor with alaminate-type photoconductive layer in such a configuration that acharge generation layer comprising a charge generating material whichcan generate a positive hole or electron when the photoconductor isexposed to light, is formed on a charge transport layer which contains acharge transporting material capable of transporting the positive-holeor electron. However, in the above-mentioned structure of thepositively-chargeable photoconductor, the charge generation layerbecomes a surface layer, so that the charge generating material, whichis fragile to external influences, for example, the application of shortwavelength light such as ultraviolet light for light exposure, coronadischarge, humidity, mechanical friction, inevitably exists in thesurface portions of the photoconductor. As a result, electrophotographicproperties deteriorate during the preservation of the photoconductor andthe image formation process. Consequently, the quality of the obtainedimages is decreased.

On the other hand, the conventional negatively-chargeable photoconductorcomprising a charge transport layer serving as a surface layer formed ona charge generation layer is scarcely subjected to the above-mentionedexternal influences. Rather, the charge transport layer formed on thecharge generation layer has an effect of protecting the chargegeneration layer.

In the positively-chargeable photoconductor, it is proposed to provideon a charge generation layer comprising a charge generating material athin protective layer comprising, for example, an insulating,transparent resin to protect the charge generation layer from theaforementioned external influences. However, when the photoconductor isexposed to light, there is a difficulty in efficiently generatingelectric charges in the charge generation layer because the lightapplied to the charge generation layer is intercepted by the protectivelayer. Therefore, the effect of light application is decreased.Furthermore, in the case where the thickness of the protective layer islarge, the photosensitivity of the photoconductor deteriorates.

As mentioned above, various proposals for obtaining thepositively-chargeable photoconductors have been made, but they have manyproblems with regard to the photosensitivity, the memory phenomenon orthe industrial hygiene.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anelectrophotographic photoconductor which comprises an electroconductivesubstrate and a photoconductive layer formed thereon, comprising acharge generating material and a charge transporting material, with highphotosensitivity and high durability.

The above-mentioned object of the present invention can be achieved byan electrophotographic photoconductor comprising an electroconductivesubstrate, a photoconductive layer formed thereon, comprising a chargegenerating material, and a vinylidene compound of formula (I): ##STR2##wherein Ar represents an aromatic group; and X represents cyano group,an alkyl group having 1 to 8 carbon atoms, or an alkoxycarbonyl grouprepresented by --COOC_(n) H_(2n+1), in which n is an integer of 1 to 8;or a vinylidene compound of formula (II):

    Ar--CH═C(COOR).sub.2                                   (II)

wherein Ar represents an aromatic group; and R represents an alkyl grouphaving 1 to 8 carbon atoms, which may form a ring in combination of twoof the alkyl groups, each of these vinylidene compounds serving as acharge transporting material.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view showing a first example of anelectrophotographic photoconductor according to the present invention;

FIG. 2 is a schematic cross-sectional view showing a second example ofan electrophotographic photoconductor according to the presentinvention;

FIG. 3 is a schematic cross-sectional view showing a third example of anelectrophotographic photoconductor according to the present invention;and

FIG. 4 is an IR absorption spectrum of 4-nitrobenzalmalononitrile foruse in Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electrophotographic photoconductor of the present inventioncomprises an electroconductive substrate, and a photoconductive layerformed thereon, comprising a charge generating material, and avinylidene compound of formula (I): ##STR3## wherein Ar represents anaromatic group; and X represents cyano group, an alkyl group having 1 to8 carbon atoms, or an alkoxycarbonyl group represented by --COOC_(n)H_(2n+1), in which n is an integer of 1 to 8; or a vinylidene compoundof formula (II):

    AR--CH═C(COOR).sub.2                                   (II)

wherein Ar represents an aromatic group; and R represents alkyl grouphaving 1 to 8 carbon atoms, which may form a ring in combination of twoof the alkyl groups, each of these vinylidene compounds serving as atransporting material.

When Ar represents an aromatic group in the above-mentioned formula (I)or (II), specific examples of the aromatic group are phenyl group; apolycyclic aromatic group such as naphthalene group, phenanthrene group,anthracene group or pyrene group; a heterocyclic aromatic group such asindole group, pyridine group, furan group, thiazole group, carbazolegroup or quinoline group; and a metallocene group such as ferrocene.

The aromatic group represented by Ar in the formulas (I) and (II) mayhave a substituent.

Specific examples of the substituent of the aromatic group representedby Ar in the formula (I) or (II) are amino group such asN,N-dimethylamino group, N,N-diethylamino group, N,N-dibenzylaminogroup, N,N-diphenylamino group, N,N-ditolylamino group, orN-tolyl-N-phenylamino group; an alkoxyl group having 1 to 8 carbon atomssuch as methoxy group, ethoxy group or benzyloxy group; hydroxyl group;an alkyl group having 1 to 8 carbon atoms such as methyl group, ethylgroup, butyl group, t-butyl group or trifluoromethyl group; a halogenatom such as fluorine, chlorine or bromine, an alkoxycarbonyl grouprepresented by --COOC_(n) H_(2n+1), wherein n is an integer of 1 to 8,such as methoxycarbonyl group, ethoxycarbonyl group, or butoxycarbonylgroup; cyano group; and nitro group.

Specific examples of the vinylidene compounds of formulas (I) and (II)according to the present invention are shown in the following Tables 1and 2. The present invention, however, is not limited by thesecompounds.

                                      TABLE 1                                     __________________________________________________________________________     ##STR4##                                                                     Compound                                                                      No.    X           Ar                                                         __________________________________________________________________________     1     CN                                                                                         ##STR5##                                                   2     CN                                                                                         ##STR6##                                                   3     CN                                                                                         ##STR7##                                                   4     CN                                                                                         ##STR8##                                                   5     CN                                                                                         ##STR9##                                                   6     CN                                                                                         ##STR10##                                                  7     CN                                                                                         ##STR11##                                                  8     CN                                                                                         ##STR12##                                                  9     CN                                                                                         ##STR13##                                                 10     CN                                                                                         ##STR14##                                                 11     CN                                                                                         ##STR15##                                                 12     CN                                                                                         ##STR16##                                                 13     CN                                                                                         ##STR17##                                                 14     CN                                                                                         ##STR18##                                                 15     CN                                                                                         ##STR19##                                                 16     CN                                                                                         ##STR20##                                                 17     CN                                                                                         ##STR21##                                                 18     CN                                                                                         ##STR22##                                                 19     CN                                                                                         ##STR23##                                                 20     CN                                                                                         ##STR24##                                                 21     CN                                                                                         ##STR25##                                                 22     CN                                                                                         ##STR26##                                                 23     CN                                                                                         ##STR27##                                                 24     CN                                                                                         ##STR28##                                                 25     CN                                                                                         ##STR29##                                                 26     CN                                                                                         ##STR30##                                                 27     CN                                                                                         ##STR31##                                                 28     CN                                                                                         ##STR32##                                                 29     CN                                                                                         ##STR33##                                                 30     CN                                                                                         ##STR34##                                                 31     CN                                                                                         ##STR35##                                                 32     CN                                                                                         ##STR36##                                                 33     CN                                                                                         ##STR37##                                                 34     CN                                                                                         ##STR38##                                                 35     CN                                                                                         ##STR39##                                                 36     CN                                                                                         ##STR40##                                                 37     COOC.sub.2 H.sub.5                                                                         ##STR41##                                                 38     COOC.sub.2 H.sub.5                                                                         ##STR42##                                                 39     COOC.sub.2 H.sub.5                                                                         ##STR43##                                                 40     COOC.sub.2 H.sub.5                                                                         ##STR44##                                                 41     COOC.sub.2 H.sub.5                                                                         ##STR45##                                                 42     COOC.sub.2 H.sub.5                                                                         ##STR46##                                                 43     COOC.sub.2 H.sub.5                                                                         ##STR47##                                                 44     COOC.sub.2 H.sub.5                                                                         ##STR48##                                                 45     COOC.sub.2 H.sub.5                                                                         ##STR49##                                                 46     COOC.sub.2 H.sub.5                                                                         ##STR50##                                                 47     COOC.sub.2 H.sub.5                                                                         ##STR51##                                                 48     COOC.sub.2 H.sub.5                                                                         ##STR52##                                                 49     COOC.sub.2 H.sub.5                                                                         ##STR53##                                                 50     COOC.sub.2 H.sub.5                                                                         ##STR54##                                                 51     COOC.sub.2 H.sub.5                                                                         ##STR55##                                                 52     COOC.sub.2 H.sub.5                                                                         ##STR56##                                                 53     COOC.sub.2 H.sub.5                                                                         ##STR57##                                                 54     COOC.sub.4 H.sub.9                                                                         ##STR58##                                                 55     COOC.sub.4 H.sub.9                                                                         ##STR59##                                                 56     COOC.sub.4 H.sub.9                                                                         ##STR60##                                                 57     COOC.sub.4 H.sub.9                                                                         ##STR61##                                                 58     COOC.sub.4 H.sub.9                                                                         ##STR62##                                                 59     COOC.sub.4 H.sub.9                                                                         ##STR63##                                                 60     COOC.sub.4 H.sub.9                                                                         ##STR64##                                                 61     COOC.sub.4 H.sub.9                                                                         ##STR65##                                                 62     COOC.sub.4 H.sub.9                                                                         ##STR66##                                                 63     COOC.sub.4 H.sub.9                                                                         ##STR67##                                                 64     COOC.sub.4 H.sub.9                                                                         ##STR68##                                                 65     COOC.sub.4 H.sub.9                                                                         ##STR69##                                                 66     COOC.sub.4 H.sub.9                                                                         ##STR70##                                                 67     COOC.sub.4 H.sub.9                                                                         ##STR71##                                                 68     COOC.sub.4 H.sub.9                                                                         ##STR72##                                                 69     COOC.sub.4 H.sub.9                                                                         ##STR73##                                                 70     COOC.sub.4 H.sub.9                                                                         ##STR74##                                                 71     COOC.sub.4 H.sub.9                                                                         ##STR75##                                                 72     COOC.sub.4 H.sub.9                                                                         ##STR76##                                                 73     COOC.sub.4 H.sub.9                                                                         ##STR77##                                                 74     COOC.sub.4 H.sub.9                                                                         ##STR78##                                                 75      COOC.sub.4 H.sub.9                                                                        ##STR79##                                                 76     COOC.sub.4 H.sub.9                                                                         ##STR80##                                                 77     COOC.sub.4 H.sub.9                                                                         ##STR81##                                                 78     COOC.sub.4 H.sub.9                                                                         ##STR82##                                                 79     COOC.sub.4 H.sub.9                                                                         ##STR83##                                                 80     COOC.sub.4 H.sub.9                                                                         ##STR84##                                                 81     COOC.sub.4 H.sub.9                                                                         ##STR85##                                                 82     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR86##                                                 83     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR87##                                                 84     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR88##                                                 85     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR89##                                                 86     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR90##                                                 87     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR91##                                                 88     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR92##                                                 89     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR93##                                                 90     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR94##                                                 91     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR95##                                                 92     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR96##                                                 93     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR97##                                                 94     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR98##                                                 95     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR99##                                                 96     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR100##                                                97     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR101##                                                98     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR102##                                                99     COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR103##                                                100    COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR104##                                                101    COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR105##                                                102    COOCH.sub.2 CH(CH.sub.3).sub.2                                                             ##STR106##                                                __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        ArCHC(COOR).sub.2            (II)                                             Compound                                                                      No.     R         Ar                                                          ______________________________________                                        103     CH.sub.3                                                                                 ##STR107##                                                 104     CH.sub.3                                                                                 ##STR108##                                                 105     CH.sub.3                                                                                 ##STR109##                                                 106     CH.sub.3                                                                                 ##STR110##                                                 107     CH.sub.3                                                                                 ##STR111##                                                 108     CH.sub.3                                                                                 ##STR112##                                                 109     CH.sub.3                                                                                 ##STR113##                                                 110     CH.sub.3                                                                                 ##STR114##                                                 111     CH.sub.3                                                                                 ##STR115##                                                 112     CH.sub.3                                                                                 ##STR116##                                                 113     CH.sub.3                                                                                 ##STR117##                                                 114     CH.sub.3                                                                                 ##STR118##                                                 115     CH.sub.3                                                                                 ##STR119##                                                 116     C.sub.4 H.sub.9                                                                          ##STR120##                                                 117     C.sub.4 H.sub.9                                                                          ##STR121##                                                 118     C.sub.4 H.sub.9                                                                          ##STR122##                                                 119     C.sub.4 H.sub.9                                                                          ##STR123##                                                 120     C.sub.4 H.sub.9                                                                          ##STR124##                                                 121     C.sub.4 H.sub.9                                                                          ##STR125##                                                 122     C.sub.4 H.sub.9                                                                          ##STR126##                                                 123     C.sub.4 H.sub.9                                                                          ##STR127##                                                 124     C.sub.4 H.sub.9                                                                          ##STR128##                                                 125     C.sub.4 H.sub.9                                                                          ##STR129##                                                 126     C.sub.4 H.sub.9                                                                          ##STR130##                                                 127     C.sub.4 H.sub.9                                                                          ##STR131##                                                 128                                                                                    ##STR132##                                                                              ##STR133##                                                 129                                                                                    ##STR134##                                                                              ##STR135##                                                 130                                                                                    ##STR136##                                                                              ##STR137##                                                 131                                                                                    ##STR138##                                                                              ##STR139##                                                 132                                                                                    ##STR140##                                                                              ##STR141##                                                 133                                                                                    ##STR142##                                                                              ##STR143##                                                 134                                                                                    ##STR144##                                                                              ##STR145##                                                 135                                                                                    ##STR146##                                                                              ##STR147##                                                 136                                                                                    ##STR148##                                                                              ##STR149##                                                 ______________________________________                                    

The vinylidene compounds of formulas (I) and (II) for use in the presentinvention can be obtained by allowing an aromatic aldehyde compound offormula (III) to react with a malonic acid derivative of formula (IV) inthe presence of a basic catalyst. ##STR150##

Specific examples of the basic catalyst for use in the above-mentionedreaction are an organic base such as pyridine, piperidine, ortriethylamine; a salt of acetic acid such as sodium acetate, potassiumacetate or ammonium acetate; and an inorganic base such as sodiumhydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

The above-mentioned reaction for preparing of the vinylidene compoundsof formulas (I) and (II) can be carried out without a solvent or in apolar solvent such as methanol, ethanol, tetrahydrofuran, 1,4-dioxane orN,N-dimethylformamide. The reaction temperature can be set the range offrom room temperature to 150° C., preferably in the range of from roomtemperature to 100° C.

The structure of the photoconductor of the present invention will now beexplained making reference to FIGS. 1 to 3.

A photoconductor shown in FIG. 1 comprises a substrate 1 and alaminate-type photoconductive layer 4 formed on the substrate 1 which isan electroconductive substrate or prepared by providing anelectroconductive layer on a sheet. The above-mentioned photoconductivelayer 4 consists of a charge generation layer 2 comprising a chargegenerating material and if necessary a binder resin, and a chargetransport layer 3 formed on the charge generation layer 2, comprising acharge transporting material and if necessary a binder resin.

The photoconductor shown in FIG. 2 further comprises a protective layer5 provided on a photoconductive layer 4.

FIG. 3 shows a cross-sectional view of a photoconductor which comprisesa single-layered type photoconductive layer 6 formed on a substrate 1,comprising a charge generating material, a charge transporting material,and if necessary a binder resin. A protective layer can also be providedon the single-layered type photoconductive layer 6, or an intermediatelayer may be interposed between the substrate 1 and the photoconductivelayer 4 or 6.

When the electrophotographic photoconductor of the present inventioncomprises a laminate-type photoconductive layer, as shown in FIGS. 1 and2, the charge transporting material is dissolved or dispersed singly inan appropriate solvent or in combination with an appropriate binderresin to obtain a coating liquid for a charge transport layer. The thusobtained coating liquid is coated on a charge generation layer anddried, so that the charge transport layer is formed on the chargegeneration layer.

Specific examples of the binder resin for the photoconductive layer foruse in the present invention are addition polymerization type resins,polyaddition type resins, and polycondensation type resins, such aspolyethylene, polypropylene, acrylic resin, methacrylic resin, vinylchloride resin, vinyl acetate resin, epoxy resin, polyurethane resin,phenolic resin, polyester resin, alkyd resin, polycarbonate resin,silicone resin, and melamine resin; copolymerization type resins whichcomprise two or more repeat units in the above-mentioned resins, such asinsulating resins of vinyl chloride - vinyl acetate copolymer resin andvinyl chloride - vinyl acetate - maleic anhydride copolymer resin; andpolymeric semiconductors such as poly-N-vinylcarbazole.

Specific examples of the solvent used in preparing the charge transportlayer are N,N-dimethylformamide, toluene, xylene, monochlorobenzene,1,2-dichloroethane, dichloromethane, 1,1,1-trichloroethane,1,1,2-trichloroethylene, tetrahydrofuran, methyl ethyl ketone,cyclohexanone, ethyl acetate, and butyl acetate.

It is preferable that 20 to 200 parts by weight of the chargetransporting material and 100 parts by weight of the binder resin becontained in the charge transport layer.

It is also preferable that the thickness of the charge transport layerbe 5 to 50 μm, more preferably 5 to 30 μm.

In the present invention, the charge generation layer can be formed byvacuum-depositing the charge generating material on theelectroconductive substrate. Alternatively, the charge generatingmaterial is dissolved or dispersed singly in an appropriate solvent orin combination with an appropriate binder resin to obtain a coatingliquid for the charge generation layer, and the thus obtained coatingliquid is coated on the electroconductive substrate and dried.

When the charge generation layer is formed by coating a dispersion ofthe charge generating material, it is preferable that the averageparticle size of the charge generating material be within the range from0.01 μm to 1 μm.

When the particle size of the charge generating material is 2 μm orless, the charge generating material can be uniformly dispersed in thesolvent, and part of the particles can be prevented from protruding overthe surface of the charge generation layer, so that the surfacesmoothness is not impaired. Therefore, electrical discharge which takesplace on the particle-protruded portion can be prevented, and the tonerfilming phenomenon, which is an adhesion of toner particles thereon,does not occur.

In addition, when the particle size of the charge generating material is0.01 μm or more, the particles do not tend to aggregate. As a result, anincrease of the resistivity of the charge generation layer and adecrease of the photosensitivity of the photoconductor can be preventedso that the photoconductor can be repeatedly used.

To prepare the charge generation layer, the charge generating materialis dispersed in the form of finely-divided particles in the solvent in aball mill or a homomixer. Then, finely-divided particles of the chargegenerating material are mixed with a binder resin and dispersed toobtain a coating liquid for the charge generation layer, and the thusobtained coating liquid is coated on the substrate. In this method offorming the charge generation layer, it is preferable that the particlesof the charge generating material be dispersed with the application ofsupersonic wave thereto so as to obtain a uniform dispersion.

As the charge generating material for use in the electrophotographicphotoconductor according to the present invention, any inorganic ororganic materials which can absorb visible light and generate freecharges can be employed.

Specific examples of such materials are inorganic materials such asamorphous selenium, trigonal-system selenium, selenium - arsenic alloy,selenium - tellurium alloy, cadmium sulfide, cadmium selenide, cadmiumsulfoselenide, mercury sulfide, lead oxide, lead sulfide, and amorphoussiliconel and organic materials such as bisazo dye, polyazo dye,triarylmethane dye, thiazine dye, oxazine dye, xanthene dye, cyaninedye, styryl dye, pyrylium dye, quinacridone dye, indigo dye, perylenedye, polycyclic quinone dye, bisbenzimidazole dye, indanthrone dye,squarylium dye, anthraquinone dye, and phthalocyanine dye.

It is preferable that 20 to 200 parts by weight of the charge generatingmaterial and 100 parts by weight of the binder resin be contained in thecharge generation layer.

It is also preferable that the thickness of the charge generation layerbe 0.1 to 10 μm, more preferably 0.5 to 5 μm.

In the case where the electrophotographic photoconductor of the presentinvention comprises a single-layered type photoconductive layer, asshown in FIG. 3, it is preferable that 20 to 200 parts by weight of thecharge generating material, 20 to 200 parts by weight of the chargetransporting material and 100 parts by weight of the binder resin becontained in the photoconductive layer.

It is also preferable that the thickness of the single-layered typephotoconductive layer be 7 to 50 μm, more preferably 10 to 30 μm.

Examples of the materials for the electroconductive substrate for use inthe present invention are a sheet, drum or foil of metals such asaluminum and nickel; a plastic film on which aluminum, tin oxide, orindium oxide is deposited; and a film or drum of paper or plastic whichis coated by an electroconductive material.

Furthermore, the previously mentioned intermediate layer which can beinterposed between the substrate and the photoconductive layer functionsas an adhesive layer or a barrier layer.

Specific examples of the material for the intermediate layer for use inthe present invention are the same resins as used in preparing thephotoconductive layer as the binder resins, and resins such as polyvinylalcohol, ethyl cellulose, carboxymethyl cellulose, vinyl chloride -vinyl acetate copolymer, vinyl chloride - vinyl acetate - maleicanhydride copolymer, casein, and N-alkoxymethyl nylon. In addition tothe above, tin oxide or indium may be dispersed in one of theabove-mentioned resins. A film prepared by deposition of aluminum oxide,zinc oxide, or silicon oxide can also be employed.

It is preferable that the thickness of the intermediate layer be 1 μm orless.

As the materials for the previously mentioned protective layer, theabove-mentioned resins are used as they are, or a material with a lowresistivity such as tin oxide or indium oxide may be dispersed in theabove-mentioned resins. In addition to the above, an organic plasmapolymerization film can be used as the protective layer. In this case,the organic plasma polymerization film may comprise oxygen, nitrogen,halogen, or an atom belonging to the group III or the group V in theperiodic table when necessary.

Other features of this invention will become apparent in the course ofthe following description of exemplary embodiments, which are given forillustration of the invention and are not intended to be limitingthereof.

SYNTHESIS EXAMPLE 1 Synthesis of 4-nitrobenzalmalononitrile (CompoundNo. 1)

A mixture of 4.53 g of commercially available 4-nitrobenzaldehyde, 2.97g of malononitrile, and two drops of piperidine was refluxed in 100 mlof methanol for 4 hours. After the completion of the reaction, the thusobtained reaction mixture was cooled, so that a solid product was formedin the reaction mixture. The solid product was separated from thereaction mixture to obtain a crude material.

The thus obtained material was recrystallized from ethanol, whereby 4.57g of 4-nitrobenzalmalononitrile (Compound No. 1) was obtained in pureform.

The melting point of the above obtained compound was 160.5° to 162.0° C.

FIG. 4 shows an IR absorption spectrum of the above compound.

SYNTHESIS EXAMPLES 2 to 28

The same procedure for preparation of the 4-nitrobenzalmalononitrile inSynthesis Example 1 was repeated except that the 4-nitrobenzaldehyde andmalononitrile used in Synthesis Example 1 were respectively replaced byvarious kinds of aromatic aldehyde compounds of formula (III) andvarious kinds of malonic acid derivatives of formula (IV), so thatvinylidene compounds of formulas (I) and (II) shown in Table 3 wereobtained. The melting point and the results of elemental analysis ofeach product are also shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                         Elemental Analysis (%)                                   Synthesis     Melting Point                                                                        C          H          N                                  Example                                                                             Compound No.                                                                          (°C.)                                                                         Found                                                                             (Calculated)                                                                         Found                                                                             (Calculated)                                                                         Found                                                                             (Calculated)                   __________________________________________________________________________    Example 1                                                                            1      160.5-162.0                                                                          60.410                                                                            (60.306)                                                                             2.605                                                                             (2.531)                                                                              21.208                                                                            (21.098)                       Example 2                                                                            3      156.0-156.5                                                                          73.895                                                                            (73.736)                                                                             2.779                                                                             (2.813)                                                                              23.565                                                                            (23.452)                       Example 3                                                                           17      182.0-183.0                                                                          73.058                                                                            (73.074)                                                                             5.559                                                                             (5.622)                                                                              21.250                                                                            (21.304)                       Example 4                                                                           24      168.6-169.5                                                                          82.486                                                                            (82.335)                                                                             3.886                                                                             (3.948)                                                                              13.716                                                                            (13.717)                       Example 5                                                                           27      210.5-211.3                                                                          85.112                                                                            (85.020)                                                                             3.843                                                                             (3.964)                                                                              11.041                                                                            (11.016)                       Example 6                                                                           28      254.0-254.5                                                                          86.417                                                                            (86.313)                                                                             3.561                                                                             (3.622)                                                                              10.169                                                                            (10.066)                       Example 7                                                                           31      145.5-146.5                                                                          75.979                                                                            (76.086)                                                                             3.557                                                                             (3.438)                                                                              20.320                                                                            (20.476)                       Example 8                                                                           34      178.5-179.0                                                                          50.872                                                                            (50.805)                                                                             1.574                                                                             (1.599)                                                                              22.390                                                                            (22.218)                       Example 9                                                                           36      98.0-99.0                                                                            63.491                                                                            (63.432)                                                                             3.700                                                                             (3.802)                                                                              10.560                                                                            (10.568)                       Example 10                                                                          37      167.5-168.0                                                                          58.575                                                                            (58.537)                                                                             3.973                                                                             (4.094)                                                                              11.420                                                                            (11.378)                       Example 11                                                                          54      124.0-125.0                                                                          61.476                                                                            (61.308)                                                                             5.054                                                                             (5.145)                                                                              10.296                                                                            (10.214)                       Example 12                                                                          55      128.0-128.5                                                                          68.580                                                                            (68.689)                                                                             5.506                                                                             (5.380)                                                                              10.415                                                                            (10.681)                       Example 13                                                                          66      150.5-151.7                                                                          79.302                                                                            (79.216)                                                                             6.522                                                                             (6.648)                                                                              6.711                                                                              (6.599)                       Example 14                                                                          72      125.0-125.5                                                                          80.396                                                                            (80.219)                                                                             5.791                                                                             (5.814)                                                                              4.167                                                                              (4.252)                       Example 15                                                                          74       99.5-100.0                                                                          81.771                                                                            (81.564)                                                                             5.274                                                                             (5.419)                                                                              3.913                                                                              (3.963)                       Example 16                                                                          78      173.7-174.5                                                                          76.342                                                                            (76.276)                                                                             6.249                                                                             (6.401)                                                                              8.024                                                                              (8.086)                       Example 17                                                                          79      129.0-130.0                                                                          54.658                                                                            (54.546)                                                                             4.569                                                                             (4.578)                                                                              10.563                                                                            (10.602)                       Example 18                                                                          81      130.5-131.3                                                                          63.650                                                                            (63.550)                                                                             5.399                                                                             (5.630)                                                                              4.106                                                                              (4.117)                       Example 19                                                                          82      141.0-141.8                                                                          61.337                                                                            (61.308)                                                                             5.049                                                                             (5.145)                                                                              10.282                                                                            (10.214)                       Example 20                                                                          83      146.0-146.5                                                                          68.742                                                                            (68.689)                                                                             5.376                                                                             (5.380)                                                                              10.617                                                                            (10.681)                       Example 21                                                                          95      78.0-79.5                                                                            80.348                                                                            (80.219)                                                                             5.760                                                                             (5.814)                                                                              4.227                                                                              (4.252)                       Example 22                                                                          96      101.0-102.0                                                                          80.273                                                                            (80.219)                                                                             5.747                                                                             (5.814)                                                                              4.239                                                                              (4.252)                       Example 23                                                                          97      122.0-123.0                                                                          81.626                                                                            (81.564)                                                                             5.375                                                                             (5.419)                                                                              3.929                                                                              (3.963)                       Example 24                                                                          100     124.0-125.5                                                                          76.257                                                                            (76.276)                                                                             6.308                                                                             (6.401)                                                                              8.121                                                                              (8.086)                       Example 25                                                                          101     134.0-135.0                                                                          54.642                                                                            (54.546)                                                                             4.635                                                                             (4.578)                                                                              10.597                                                                            (10.602)                       Example 26                                                                          103     87.5-89.0                                                                            54.251                                                                            (54.344)                                                                             4.102                                                                             (4.181)                                                                              5.176                                                                              (5.281)                       Example 27                                                                          111     104.5-105.3                                                                          75.034                                                                            (74.988)                                                                             4.956                                                                             (5.035)    --                             Example 28                                                                          128     213.0-214.0                                                                          56.388                                                                            (56.322)                                                                             3.987                                                                             (4.000)                                                                              4.940                                                                              (5.052)                       __________________________________________________________________________

EXAMPLE 1 Formation of Charge Generation Layer

5 parts by weight of a bisazo dye of formula (A), 2.5 parts by weight ofa commercially available butyral resin (Trademark "Denka Butyral Resin#3000-2", made by Denki Kagaku Kogyo K. K.), and 92.5 parts by weight oftetrahydorfuran were dispersed in a ball mill for 12 hours. ##STR151##

Tetrahydrofuran was further added to the thus obtained mixture in suchan amount that the obtained dispersion might have a concentration of 2wt. %, and the above mixture was dispersed again to prepare a coatingliquid for a charge generation layer. The thus obtained coating liquidwas coated by a doctor blade on an aluminum-deposited surface of analuminum-deposited polyester film with a thickness of 100 μm serving asa substrate, and dried, so that a charge generation layer with athickness of 1.0 μm was formed on the substrate.

Formation of Charge Transport Layer

6 parts by weight of the Compound No. 1 prepared in Synthesis Example 1,10 parts by weight of a polycarbonate resin (Trademark "K-1300", made byTeijin Chemicals Ltd.), 0.002 parts by weight of a methylphenyl -silicone (Trademark "KF50 100CPS", made by Sin-Etsu Chemical Co,. Ltd.),and 94 parts by weight of tetrahydrofuran were mixed to prepare acoating liquid for a charge transport layer. The thus obtained coatingliquid was coated by the doctor blade on the above obtained chargegeneration layer, and dried, so that a charge transport layer with athickness of 20.0 μm was formed on the charge generation layer. Thus, alaminate-type electrophotographic photoconductor No. 1 comprising analuminum electroconductive substrate, the charge generation layer andthe charge transport layer of the present invention was obtained.

EXAMPLES 2 to 13

The procedure for preparation of the electrophotographic photoconductorNo. 1 in Example 1 was repeated except that the Compound No. 1 for usein the coating liquid for the charge transport layer in Example 1 wasreplaced by each of the vinylidene compounds shown in Table 1, wherebylaminate-type electrophotographic photoconductors No. 2 to No. 13 of thepresent invention was obtained.

EXAMPLE 14

The procedure for preparation of the electrophotographic photoconductorNo. 1 in Example 1 was repeated except that 5 parts by weight of thebisazo dye of formula (A) for use in the coating liquid for the chargegeneration layer and the Compound No. 1 for use in the coating liquidfor the charge transport layer used in Example 1 were respectivelyreplaced by 6 parts by weight of a trisazo dye of formula (B) and theCompound No. 3 prepared in Synthesis Example 2 shown in Table 3, wherebya laminate-type electrophotographic photoconductor No. 14 of the presentinvention was obtained. ##STR152##

EXAMPLES 15 to 31

The procedure for preparation of the electrophotographic photoconductorNo. 14 in Example 14 was repeated except that the Compound No. 3 for usein the coating liquid for the charge transport layer used in Example 14was replaced by each of the vinylidene compounds shown in Table 3,whereby laminate-type electrophotographic photoconductors No. 15 to No.31 of the present invention were obtained.

EXAMPLE 32 Formation of Charge Generation Layer

A mixture of 5 parts by weight of titanylphthalocyarline (TiPc), 5 partsby weight of a polyvinyl butyral resin (Trademark "S-Lec BLS", made bySekisui Chemical Co., Ltd.), and 90 parts by weight of tetrahydrofuranwas dispersed in a ball mill for 12 hours. Tetrahydrofuran was furtheradded to the thus obtained mixture in such an amount that the obtaineddispersion might have a concentration of 2 wt. %, and the above mixturewas dispersed again to prepare a coating liquid for a charge generationlayer. The thus obtained coating liquid was coated by a doctor blade onan aluminum-deposited surface of an aluminum-deposited polyester filmwith a thickness of 100 μm serving as a substrate, and dried, so that acharge generation layer with a thickness of 0.5 μm was formed on thesubstrate.

Formation of Charge Transport Layer

6 parts by weight of the Compound No. 24 prepared in Synthesis Example 4shown in Table 3, 10 parts by weight of a polycarbonate resin (Trademark"K-1300", made by Teijin Chemicals Ltd.), and 94 parts by weight oftetrahydrofuran were mixed to prepare a coating liquid for a chargetransport layer. The thus obtained coating liquid was coated on theabove obtained charge generation layer by the doctor blade, and dried,so that a charge transport layer with a thickness of 20.0 μm was formedon the charge generation layer. Thus, a laminate-typeelectrophotographic photoconductor No. 32 comprising an aluminumelectroconductive substrate, the charge generation layer and the chargetransport layer of the present invention was obtained.

EXAMPLES 33 to 42

The procedure for preparation of the electrophotographic photoconductorNo. 32 in Example 32 was repeated except that the Compound No. 24 foruse in the coating liquid for the charge transport layer used in Example32 was replaced by each of the vinylidene compounds shown in Table 3,whereby laminate-type electrophotographic photoconductors No. 33 to No.42 of the present invention were obtained.

Each of the thus prepared electrophotographic photoconductors No. 1 toNo. 42 according to the present invention was positively charged underapplication of +6 kV of corona charge, using a commercially availableelectrostatic copying sheet testing apparatus ("SP-428", made byKawaguchi Electro Works Co., Ltd.). Then, each electrophotographicphotoconductor was allowed to stand in the dark for 20 seconds withoutapplying any charge thereto, and the surface potential Vo (V) of thephotoconductor was measured. Each photoconductor was then illuminated bya tungsten lamp in such a manner that the illuminance on the illuminatedsurface of the photoconductor was 40 lux, and the exposure E_(1/2)(lux·sec) required to reduce the initial surface potential Vo (V) to 1/2thereof was measured. The results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Ex-   Photo-     Charge    Com-                                               ample conductor  Generating                                                                              pound  Vo   E.sub.1/2                              No.   No.        Material  No.    (V)  (lux·sec)                     ______________________________________                                        Ex. 1  1         A          1     1192 52.3                                   Ex. 2  2         A         24     1761 63.9                                   Ex. 3  3         A         31     1765 115.8                                  Ex. 4  4         A         37      736 22.8                                   Ex. 5  5         A         54     1892 25.8                                   Ex. 6  6         A         55     1633 29.4                                   Ex. 7  7         A         74     1850 12.2                                   Ex. 8  8         A         79     1817 43.1                                   Ex. 9  9         A         82     2281 26.1                                   Ex. 10                                                                              10         A         83     2247 22.1                                   Ex. 11                                                                              11         A         96     2431 23.8                                   Ex. 12                                                                              12         A         97     1762 31.7                                   Ex. 13                                                                              13         A         101    2183 76.1                                   Ex. 14                                                                              14         B          3     1830 95.7                                   Ex. 15                                                                              15         B         24     1578 76.2                                   Ex. 16                                                                              16         B         27     1887 48.0                                   Ex. 17                                                                              17         B         34     1909 121.4                                  Ex. 18                                                                              18         B         37      558 14.5                                   Ex. 19                                                                              19         B         54     1416 43.1                                   Ex. 20                                                                              20         B         55     1248 30.6                                   Ex. 21                                                                              21         B         66     1976 145.6                                  Ex. 22                                                                              22         B         72     2104 68.1                                   Ex. 23                                                                              23         B         74     1726 25.7                                   Ex. 24                                                                              24         B         79     1913 63.2                                   Ex. 25                                                                              25         B         82     1628 54.3                                   Ex. 26                                                                              26         B         83     2043 38.9                                   Ex. 27                                                                              27         B         95     2187 128.4                                  Ex. 28                                                                              28         B         96     2262 47.2                                   Ex. 29                                                                              29         B         97     1956 35.0                                   Ex. 30                                                                              30         B         100    2252 150.7                                  Ex. 31                                                                              31         B         101    1893 76.2                                   Ex. 32                                                                              32         TiPc      24     1424 66.0                                   Ex. 33                                                                              33         TiPc      37      719 22.4                                   Ex. 34                                                                              34         TiPc      54     1138 37.5                                   Ex. 35                                                                              35         TiPc      55     1107 25.4                                   Ex. 36                                                                              36         TiPc      74     1720 13.9                                   Ex. 37                                                                              37         TiPc      79     1532 65.0                                   Ex. 38                                                                              38         TiPc      82     1319 36.7                                   Ex. 39                                                                              39         TiPc      83     1829 34.1                                   Ex. 40                                                                              40         TiPc      96     1837 40.6                                   Ex. 41                                                                              41         TiPc      97     1468 26.0                                   Ex. 42                                                                              42         TiPc      101    1799 46.1                                   ______________________________________                                    

The vinylidene compounds used as the charge transporting materials inthe electrophotographic photoconductor of the present invention can beprepared by a relatively simple and effective method, and excellentlydissolved or dispersed in a binder resin. Furthermore, the vinylidenecompounds can function as charge transporting materials capable ofeffectively accepting and transporting the electrical charges which aregenerated in a charge generation layer. Accordingly, theelectrophotographic photoconductors comprising the vinylidene compoundsas the charge transporting materials according to the present inventionhave high photosensitivity and high durability, and can readily bringabout the dark decay.

What is claimed is:
 1. An electrophotographic photoconductorcomprising:an electroconductive substrate; and a photoconductive layerformed thereon, comprising a charge generating material, and avinylidene compound serving as a charge transporting material, which isselected from the group consisting of a vinylidene compound of formula(I): ##STR153## wherein Ar represents a metallocene group; and Xrepresents cyano group, an alkyl group having 1 to 8 carbon atoms, or analkoxycarbonyl group represented by --COOC_(n) H_(2n+1), in which n isan integer of 1 to 8; and a vinylidene compound of formula (II):

    Ar--CH═C(COOR).sub.2                                   (II)

wherein Ar represents a metallocene group; and R represents an alkylgroup having 1 to 8 carbon atoms, which may form a ring in combinationof two of said alkyl groups.
 2. The electrophotographic photoconductoras claimed in claim 1, wherein said photoconductive layer furthercomprises a binder resin.
 3. The electrophotographic photoconductor asclaimed in claim 1, wherein said binder resin is selected from the groupconsisting of polyethylene, polypropylene, acrylic resin, methacrylicresin, vinyl chloride resin, vinyl acetate resin, epoxy resin,polyurethane resin, phenolic resin, polyester resin, alkyd resin,polycarbonate resin, silicone resin, melamine resin, vinyl chloride -vinyl acetate copolymer resin, vinyl chloride - vinyl acetate - maleicanhydride copolymer resin, and poly-N-vinylcarbazole.
 4. Theelectrophotographic photoconductor as claimed in claim 1, wherein saidphotoconductive layer comprises 20 to 200 parts by weight of said chargegenerating material, 20 to 200 parts by weight of said vinylidenecompound serving as a charge transporting material, and 100 parts byweight of said binder resin.
 5. The electrophotographic photoconductoras claimed in claim 4, wherein said photoconductive layer has athickness of 7 to 50 μm.
 6. The electrophotographic photoconductor asclaimed in claim 1, wherein said photoconductive layer comprises acharge generation layer comprising said charge generating material and acharge transport layer comprising said vinylidene compound serving as acharge transporting material, with one of said two layers being overlaidon the other.
 7. The electrophotographic photoconductor as claimed inclaim 6, wherein said charge transport layer further comprises a binderresin.
 8. The electrophotographic photoconductor as claimed in claim 7,wherein said charge transport layer comprises 20 to 200 parts by weightof said vinylidene compound serving as a charge transporting material,and 100 parts by weight of said binder agent.
 9. The electrophotographicphotoconductor as claimed in claim 8, wherein said charge transportlayer has a thickness of 5 to 50 μm.
 10. The electrophotographicphotoconductor as claimed in claim 6, wherein said charge generationlayer further comprises a binder agent.
 11. The electrophotographicphotoconductor as claimed in claim 9, wherein said charge generationlayer comprises 20 to 200 parts by weight of said charge generatingmaterial, and 100 parts by weight of said binder agent.
 12. Theelectrophotographic photoconductor as claimed in claim 11, wherein saidcharge generation layer has a thickness of 0.1 to 10 μm.
 13. Theelectrophotographic photoconductor as claimed in claim 6, wherein saidcharge generating material is selected from the group consisting ofamorphous selenium, trigonal-system selenium, selenium - arsenic alloy,selenium - tellurium alloy, cadmium sulfide, cadmium selenide, cadmiumsulfoselenide, mercury sulfide, lead oxide, lead sulfide, amorphoussilicone, bisazo dye, polyazo dye, triarylmethane dye, thiazine dye,oxazine dye, xanthene dye, cyanine dye, styryl dye, pyrylium dye,quinacridone dye, indigo dye, perylene dye, polycyclic quinone dye,bisbenzimidazole dye, indanthrone dye, squarylium dye, anthraquinonedye, and phthalocyanine dye.
 14. The electrophotographic photoconductoras claimed in claim 1, further comprising a protective layer provided onsaid photoconductive layer.
 15. The electrophotographic photoconductoras claimed in claim 1, further comprising an intermediate layer providedbetween said electroconductive substrate and said photoconductive layer.16. The electrophotographic photoconductor as claimed in claim 15,wherein said intermediate layer has a thickness of 1 μm or less.